The Centers for Disease Control and Prevention estimates that each year in the United States Salmonella species cause 1.2 million illnesses, of which 23,000 require hospitalization and 450 result in death. As seen for numerous bacterial pathogens, the incidence of multidrug resistant Salmonella infections is rising dramatically. There is a clear need for the definition of novel bacterial targets for the design of new antimicrobials and it has been well argued that targeting virulence factors instead of essential cell components will lead to weaker selection for resistance to the new drugs. This proposed project characterizes a RNA repair system in Salmonella enterica subsp. enterica serovar Typhimurium that is likely to control expression of virulence factors required for survival of stres conditions encountered during infection. Since the RNA repair system is conserved in many bacterial pathogens, its characterization may reveal new targets for broad-spectrum antimicrobials. The specific aims of this project are to: Aim 1- define the components of the RNA repair system and their substrates, and Aim 2- characterize the roles the RNA repair system plays in the cellular response to stress. The approaches to accomplish these aims include: define the protein/RNA components and RNA substrates of the RNA repair system using mass spectrometry analysis and RNA sequencing of ribonucleoprotein complexes that co-immunoprecipitate with FLAG-tagged RNA ligase, RNA 3'phosphate cyclase, and Ro-sixty-related protein that are encoded by the RNA repair operon of S. Typhimurium; find interacting partners with the RNA repair proteins using a synthetic lethal screen; confirm interactions of RNA and protein from RNA repair ribonucleoprotein complexes using biolayer interferometry and surface plasmon resonance; employ next-generation RNA sequencing and proteomic analysis by mass spectrometry to determine changes in gene expression mediated by the RNA repair system; exploit Northern blot analyses to reveal repair of identified RNA substrates for the RNA repair system; and reveal the cellular signal for activation of the RNA repair system by refining the repertoire of stress conditions that induce expression of the RNA repair proteins.